Automatic refrigerator defroster



Dec. 15, 1936. A. s. VOLPIN AUTOMATIC REFRIGERATOR DEFROSTER Filed Aug. 27 1 MN mm m M A Patented Dec. 15, 1936 UNITED STATES PATENT OFFICE 2,084,396 AUTOMATIC REFRIGERATOR DEFROSTER Delaware Application August 27, 1934, Serial No. 741,635

14 Claims.

The invention relates to a device for automatically controlling the defrosting of mechanical refrigerators, and particularly to a. device which will effect defrosting at a convenient period.

It is one of the objects of the invention to provide a defrosting mechanism which will operate to cut off the refrigerating unit so that the coils will be defrosted at a convenient period, such as the early morning hours.

Another object of the invention is to provide the combination of an automatic defrosting device which is actuated by delay mechanism so that the defrosting operation will occur a substantial period after the active use of the refrigerator.

Another object of the invention is to provide a control unit for a defrosting device such that the control unit will only operate to effect the defrosting operation at a desired interval.

It is also an object of the invention to provide a unit which will control the defrosting operation a predetermined period after the closing of the refrigerator.

A still further object of the invention is to .provide a defrosting device wherein the defrosting operation is instituted when the box is not being opened and hence at a period when no specific freezing operation is required of the cooling unit.

Other and further objects of the invention will be readily apparent when the following description is considered in connection with the accompanying drawing, wherein:

Fig. 1 is a transverse sectional view of a refrigerator of ordinary construction. which has been equipped with the automatic defrosting attachment.

Fig. 2 is a detailed broken view of the switch mechanism and its manner of manipulation.

Fig. 3 is a top plan view looking down on the switch mechanism of Fig. 2.

Fig. 4 is a wiring diagram of the device.

In the use of mechanical refrigerators it is well known that condensation of the moisture in the box occurs to such an extent that the frost accumulates on the coils interfering seriously with the efliciency and operation thereof. It is the usual practice to manually cut off the current to the refrigerating unit so that the temperature of the coil is permitted to rise to such an extent that the frost will melt from the coil.

This manipulation of the refrigerating unit is troublesome and in many instances is overlooked or neglected so that the desired efflciency of many refrigerators is not obtained; Some attempt has been made to provide automatic defrosting devices, but the present invention contemplates a defrosting device which will be actuated only after a predetermined period and will thus be effective at a time when the box is not being opened.

A portion of a refrigerator box is shown at 2 and as is usual is provided with the inner lining 3 and the outer cover 4 of metal or other suitable material. The door by which access is had to the refrigerator, is shown at 5 and is hinged at 6 for opening movement. The refrigerator coils are shown generally at 8.

In order to cut off the refrigerating unit to defrost the evaporator or cooling element 8 at an opportune time when no particular freezing operation is desired of the box, or when the box is not being entered frequently, a thermostat 20 is provided and positioned in a heat storage device 2|. This heat storage device 2| is in the form of a block of insulating material which carries a body of suitable material such as soft iron 24. This iron core is arranged to be heated by an electric resistance element 23 and is insulated therefrom by suitable mica plates 22, or otherwise as is usual with such construction. The current to the resistance element 23 is arranged to pass through a bimetallic thermostat contact 26 of a type which is well known and which is of such a construction that if the resistance element 23 reaches a predetermined temperature then no further current will pass through the contact 26.

The switch for controlling the flow of current to the resistance element 23 is seen at 30. This switch is of the plunger type wherein a plunger 3| is normally pressed forwardly by a spring 32 in such a manner that it is contacted by the door 34. As is seen in Fig. 1, when the door 5 is closed the plunger 3| will be depressed to open the switch 30 so that there will be no flow of current into the resistance element 23. When, however, the door 5 is opened the plunger 3| will move forwardly to close the switch 30 and the flow of current will heat the resistance element 23. The heating of this element 23, of course, effects a corresponding rise in temperature in the thermostat 20 so that the thermostat is maintained in a more or less heated condition in accordance with the frequency of opening the refrigerator door. The resistance element 23 and core 24 are buried in the insulation 2| and shielded thereby to such an extent that the heat imparted to the core be retained for a conis not concerned with defrosting at all. The

siderable period of time-approximating three or four hoursor more. This structure serves as a delay mechanism for preventing the thermostat 20 from operatinguntil a considerable or. predetermined period after the door Sis last closed. It is intended that the intermittent open- 'ing of the door 5 during he day and during the time when the boxis being entered will cause the intermittent heating of the element 23 tomaintain the thermostat 20 heated. When, however, the boxhas been closed for a considerable period the'core 24 and the thermostat 20 will gradually cool off, so that the sylphon bellows 35 of the thermostat will be caused to contract.

The bellows 35 of the expansible fluid thermo stat 20 is best seen in Fig. 2 and is suitably supported in the switch box 4|. Connected to the end of the element 35 is a bracket 31 and a trip latch 38. This latch is normally held in the position shown in Fig. 2 by a spring 39 and a stop finger". When the thermostat 20 cools off, contraction of the bellows 35 carries the trip latch 33 downwardly .so that the shoulder 42 thereof will cause a corresponding movement in the switch 44 so that the switch will be moved to the dotted line position of Fig. 2. During this movement, however, the support 36 remains stationary and the stop finger 4|! will slide along the inclined face to cause tilting of the latch 38 so that the shoulder 42 will release the switch 44. As long as the thermostat 20 remains cool the device cannot be reset to trip the switch 44 because the latch 33 is held inoperative. When, however, the resistance element 23 is reheated the bellows 35 will expand and the latch 38 will assume its position shown in Fig. 2. Thus there will be but a single cut off of the unit unless the door is again opened toenergize the resistance 23.

The switch 44, as seen in Fig. 4, controls the operation of the refrigerating unit insofar as 3 this invention is concerned and when it is moved to the dotted line position of Fig. 2 the operation of the unit is cut off and the defrosting operation will begin. When the defrosting operation .has been completed and the temperature of the coil 8 has been increased to such an extent that a thermostat l2 located adjacent the cooling coil 3 will be caused to act, then the refrigerating unit is again turned on by expansion of the bellows 50 contacting the end 54 of the switch 43 to move it to the full line position of Fig. 2.

A tray or pan of some sort is usually positioned beneath the refrigerating coil so that the moisture dripping from the coil during the defrosting operation may be trapped, or it may be led into a suitable drain and in some manner removed from the refrigerator.

The invention contemplates a completely automatic defrosting device which will operate only' after a predetermined interval during which the refrigerator has remained closed. This interval is determined by the period elapsing during which the temperature of the device 2| will be reduced to such an extent as to cause contraction of the thermostat 20. One thermostat 23,

primary advantage of the invention, however, is that the defrosting occurs at a most opportune time when no quick freezing is necessary and when it will cause the least inconvenience.

The present mechanism is provided in addition to the regular electric circuits in the refrigerator which effect the ordinary operation thereof. While an electric resistance or delay has been shown and described any suitable, mechanical, chemical or electrical delay device may be incorporated in the attachment as equivalent of the resistance 23 and heat retaining core 24 because the invention contemplates broadly any suitable delay device.

Having described the invention, what is claimed is:

1. A defrosting mechanism for refrigerators including an electrical circuit, a resistance in the circuit, a switch in the circuit, means operable upon opening of the refrigerator door to close the switch to heat said resistance, and additional means operable upon cooling of said resistance to eifect defrosting of the refrigerator coil.

2. An automatic defrosting mechanism for mechanical refrigerators including means operable at a predetermined interval after the closing of the refrigerator door to cut out the refrigerating unit, and means to cut in the refrigerating unit when defrosting is completed.

3. In an automatic refrigerator defrostig device, a cut out thermostat, a cut in thermostat, and delay means to actuate said first thermostat so that the refrigerator will be cut off to initiate defrosting a predetermined time after instigation of operation of said means.

4. In an automatic refrigerator defrosting device, a cut out thermostat, a cut in thermostat, and delay means to actuate said first thermostat so that defrosting will be initiated after a predetermined period following the closing of the refrigerator door.

5. A refrigerator defrosting delay control device including an electrical resistance, a metal body adapted to be heated thereby, a thermostat to be heated by said body, and a control member on said thermostat to be moved thereby after a delay equal to the period of cooling of said body.

6.'A defroster control for refrigerators of a type to cause defrosting when the refrigerator is not being opened and closed, including an electric resistance, means to be heated thereby when the refrigerator door is opened, a thermostat to be heated by said means and to be cooled by the refrigerator, and additional means to cut of! the refrigerating unit to effect defrosting only after said thermostat has cooled.

7. A defroster for refrigerators to effect defrosting in the early morning hours when the refrigerator is not being entered including a delay control device, means to energize said device to retain it inoperative while the refrigerator is being entered whereby a predetermined period will elapse after the entering of the refrigerator before defrosting will occur.

8. A defroster for refrigerators to eflect defrosting in the early morning hours when the refrigerator is not being entered including a delay control device, means to energize said device to retain it inoperative while the refrigerator is being entered whereby a predetermined period will elapse after the entering of the refrigerator before defrosting will occur, and ad- 15 including a thermostat to cut off the refrigerat-' ing unit, a thermostat to turn on the refrigeratditional means to start refrigeration after defrosting.

9. A control device for a refrigerator including means operative to modify normal operation of the refrigerator to permit melting of frost thereon, and appreciably later than when said means is placed in its initial operative condition, and means for intermittently placing said first means in its initial operative condition, whereby modified operation of the refrigerator is effected only when a period between operation of said second means exceeds the time delay period of said first means.

10. In a refrigerator having a door, a control device including means operative to modify normal operation of the refrigerator to permit melting of frost thereon, and appreciably later than when said means is placed in its initial operative condition, and means for intermittently placing said first means in its initial operative condition each time said door is opened, whereby modified operation of the refrigera tor is effected only when a period between door opening operations exceeds the time delay period of said first means.

11. A defrosting attachment for refrigerators including a thermostat to cut off the refrigerating unit, a thermostat to turn on the refrigerating unit after defrosting has terminated, and means controlling the first thermostat so that the refrigerating unit will be out off to initiate defrosting only upon a predetermined delay after initiating operation of said control means.

12. A defrosting attachment for refrigerators ing unit after defrosting has terminated, and means controlling the first thermostat so that the refrigerating unit will be out off to initiate defrosting only upon a predetermined delay producing cold, an electric circuit, means for changing the condition of said circuit each time said door is opened, andmeans associated with said electric,circuit operative after a predetermined length of time after said door has been opened for modifying the operation of said unit to initiate a defrosting period and permit melting of frost on said evaporator.

14. A refrigerator having a chamber provided with a door, a refrigerating unit including an evaporator disposed within the chamber for producing cold, an electric circuit, means for closing and opening said circuit each time said door is opened and subsequently closed, and means associated with said electric circuit operative after'a period of delay after said door has been opened and subsequently closed for stopping the operation of said unit to initiate a defrosting period and permit melting of frost on said evaporator.

' 2 ALEXANDER S. VOLPIN. 

